1. Field of The Invention
The present invention relates to a toner carrier and an image formation apparatus using the same. More particularly, the present invention is concerned with a toner carrier which is intended to form a visible image on the surface of an image formation body by supplying a toner to the image formation body such as a photosensitive body, paper or the like that preserves an electrostatic latent image in an image formation apparatus such as copying machinery, printers or the like, and which affords a high quality image free from image unevenness, is also minimized in variation of its characteristics during a long-term service, and is excellent in durability. The present invention also relates to an image formation apparatus using the same.
2. Description of the Related Arts
In regard to an electrophotographic image formation method including copying machinery, printers or the like, there is previously known a pressurized developing method as an image formation method which comprises supplying a unary toner to an image formation body such as a photosensitive body preserving an electrostatic latent image, and visualizing the latent image by allowing the toner to adhere to the latent image (refer to U.S. Pat. Nos. 3,152,012 and 3,731,146).
The pressurized developing method, which performs the image formation by bringing a toner carrier that supports a toner into contact with an image formation body such as a photosensitive body preserving an electrostatic latent image, and allowing the toner to adhere to the latent image on the aforesaid image formation body, thus requires the above-mentioned toner carrier to be constituted of an electroconductive elastic body having both electroconductivity and elasticity.
Specifically in the foregoing pressurized developing method the constitution is such that, for instance, as illustrated in FIG. 2, a toner carrier 1 (developing roller) is placed between a toner application roller 5 for supplying a toner and an image formation body 6 (photosensitive body, etc.) preserving an electrostatic latent image; the toner carrier 1 (developing roller), the image formation body 6 (photosensitive body, etc.) and the toner application roller 5 rotate each in the direction of the arrow in FIG. 2, thereby a toner 7 is supplied onto the surface of the toner carrier 1 (developing roller) with the toner application roller 5; the toner carrier 1 (developing roller) rotates, while being in contact with the image formation body 6 (photosensitive body, etc.) in a state that the toner is arranged into a uniform thin film by a layer forming blade 8; and the toner thus formed into a thin film is allowed to adhere to a latent image on the image formation body 6 (photosensitive body, etc.) from the toner carrier 1 (developing roller), whereby the aforesaid latent image is visualized.
In such image formation apparatus by means of pressurized developing system as the above, the toner carrier 1 is obliged to rotate, while maintaining the state of close contact with the image formation body 6. For this reason, the constitution of the toner carrier 1 is such that as illustrated on the schematic cross section of the attached FIG. 1, a shaft 6 consisting of an electroconductive material such as a metal is equipped on its outside periphery with an electroconductive elastic layer 3 composed of an electroconductive elastic body which is imparted with electroconductivity by blending an electroconductivity imparting agent in elastic rubber such as silicone rubber, acrylonitrile butadien rubber, ethylene propylene rubber and polyurethane rubber or foam thereof. In addition, a coating layer 4 composed of a resin or the like is installed on the surface of the electroconductive elastic layer 3 for the purpose of controlling electrostatic property and adhesivity for the toner, controlling force of friction between the image formation body and the layer forming blade, or preventing fouling of the image formation body due to the elastic body.
On the other hand, a proposal is made on an image formation method for forming an image by allowing a toner supported on a toner carrier to directly jump over onto an image formation body composed of paper sheets such as paper, OHP paper sheet or the like via a perforated controlling electrode.
Another proposal is also made on a method for forming an image by supporting a non-magnetic toner layered into thin layer on the surface of a toner carrier which is in the form of sleeve and which is placed in a non-contact state in the vicinity of a photosensitive body, and allowing the toner to jump over onto the photosensitive body to form images {refer to Japanese Patent Application Laid Open No. 116559/1983 (Showa 58)}.
In both the above-mentioned methods, the electroconductive elastic layer for a toner carrier is equipped on the surface thereof with a coating layer composed of a resin or the like for the purpose of controlling electrostatic property and adhesivity for the toner, or decreasing force of friction with an other member such as the photosensitive body, layer forming blade, controlling electrode and the like.
It has been suggested by the present inventors that the friction and image characteristics can be improved by a toner carrier wherein such a resin as melamine resin, phenolic resin, alkyd resin, fluororesin and polyamide resin is employed in a coating layer.
However, accompanying the major currents in recent years towards high speed of a printer, improvement required of image fineness, colored image and the like, the requirements for image forming properties have come to be increasingly strict, thus actualizing a variety of problems with which conventional toner carriers can no longer cope. In particular, the problems still remain unsolved in that (a) an increase in toner damage caused by high speed tendency is grasped as an important problem which leads to defective image such as fog due to poor electrification of a toner upon long-term service of a toner carrier, and (b) while the demand for evenness in image quality is increasingly accentuated, there take place such defective images as fogging of white image, unevenness in half tone image and unevenness in density of black image accompanying increase in the number of printing sheets in the case of long-term service of a toner carrier by incorporating it in an image formation apparatus.
With respect to the durability of the toner carrier, there are caused as the case may be, the problems in that agglomerated toner which brings about filming or fusedly fixing attributable to toner damage scrapes off and wears the toner carrier or a member in contact therewith, thereby inducing toner leakage.
Appropriate elimination of damaged toner is the drastic measure of solving against various problems attributable to toner damage, but it is difficult with the state of the art to completely remove damaged toner from a developing system. In this case, as the countermeasure from the side of the toner carrier it is one of effective means for suppressing toner damage to decrease the hardness of the toner carrier so as to absorb as much as possible the pressure of contact with other members. On the other hand, however, it is known that in the case of the toner carrier being flexible and markedly low in hardness, when such carrier is incorporated in a printer or the like and is used for imaging after a long-term non-use state, deformation remains which is due to press contact between the carrier and a layer forming blade in half tone image, sometimes causing streaky trace (defective set image). On the basis of the knowledge, it is taken into consideration to adopt a method for enhancing wear resistance of the toner carrier by increasing the hardness thereof to the utmost, while limiting the the quantity of deformation due to press contact therebetween. Nevertheless in such a case, the stress applied to a toner is extremely increased, thus giving rise to an increase in damaged toner. As a result, variation in the electrification characteristics of the toner takes place, whereby a markedly adverse influence upon the image characteristics is almost impossible to prevent.
Moreover, it is the drastic measure of solving against toner leakage due to the wear of the toner carrier to prevent filming or fusedly fixing of the toner. However, owing to the design trend towards shifting the glass transition temperature of a toner to the lower side from the preference for energy saving in recent years, the solution of the present subject is increasingly made difficult. In such circumstances it is thought that importance should be attached to such design concept as excluding to the utmost, the factors for causing agglomerated toner as the countermeasure from the side of the toner carrier.
The present invention has been made in such circumstances. That is to say, a general object of the present invention is to provide a toner carrier which is capable of suppressing toner damage, preventing another evilness caused by suppression of toner damage such as defective image, and affording steadily favorable image even in a working environment more prone to cause defective image including long-term preservation and long-term service; and to provide an image formation apparatus in which use is made of the above-mentioned toner carrier.
Another object of the present invention is to provide a toner carrier which is capable of suppressing a toner carrier from being scraped off by agglomerated toner attributable to toner damage, preventing the generation of a defect such as toner leakage, and affording steadily favorable image even in a working environment more apt to cause defective image including long-term preservation and long-term service; and to provide an image formation apparatus in which use is made of the above-mentioned toner carrier.
Still another object of the present invention is to provide a toner carrier which is capable of affording further high quality image, and which is excellent in durability without causing fogging of white image, roughness in half tone image or unevenness in density of black image even during long-term service; and to provide an image formation apparatus in which use is made of the above-mentioned toner carrier.
Further objects of the present invention will be obvious from the content of the specification hereinafter disclosed.
In such circumstances, intensive research and development were accumulated by the present inventors in order to solve the aforesaid problems. As a result, it has been found that toner damage is suppressed, another evilness caused by suppression thereof is prevented and at the same time, steadily favorable image is obtainable even in a working environment more prone to cause defective image including long-term preservation and long-term service by regulating the physical properties of the surface of the toner carrier so that the xe2x80x9cZ-valuexe2x80x9d as mentioned hereinafter is made to be in the under-mentioned range, said value being obtained from the measurement of deformation restoration behavior of the surface of the toner carrier at the time of measuring the universal hardness.
Specifically, the universal hardness is obtained by the procedure comprising pushing a penetrator in the form of a quadrangular pyramid or a triangular pyramid in the surface of an object to be measured under a prescribed test load applied thereto, finding the surface area of contact between the penetrator and the object to be measured from the pushed-in depth of the penetrator, and finding the hardness from the surface area and the test load. In this case it is also possible to calculate the values of elastic energy and plastic energy among the energies in relation to the deformation of the surface of the object to be measured and also the ratio of each of the energies by pushing any of the above-mentioned penetrator in the object to be measured, and thereafter gradually decreasing the test load applied by the penetrator. In the present invention, it has been found that defective set image can be prevented by regulating the relation between the elastic energy value and the plastic energy value to a specific range. The point to which special attention should be paid is that the viscoelastic characteristics in the vicinity of the surface of the toner carrier contributes to set resistance and also wear resistance of the toner carrier, more than the hardness as measured by Asker C hardness for the whole toner carrier. In the present invention it has also been found that, as the result of investigation on numerical evaluation of the viscoelastic characteristics in the vicinity of the surface of the toner carrier, the viscoelastic characteristics can be evaluated by the xe2x80x9cZ-valuexe2x80x9d as mentioned hereinafter. The present invention has been accomplished by the foregoing findings and information.
It has also been found that the wear of the toner carrier is caused by the agglomerated toner which penetrates in the portion where the toner carrier and sealant of a toner cartridge are in press contact with each other, and accelerates scraping throughout the action of the toner carrier. It is thought that deformation takes place at the portion of press contact during the toner carrier stands still, and immediately after the start of action thereof slight clearance due to residual deformation is generated between the sealant, thereby causing toner to penetrate therein and generating agglomerated toner owing to press contact and friction. It has been presumed from the foregoing by the present inventors that in the case where the toner carrier assumes plastic deformation behavior over a reference value, the probability that the slight clearance is generated is increased, thereby promoting the penetration of the agglomerated toner into the portion of press contact.
Moreover, intensive research and investigation were set forward by the present inventors in the light of the aforesaid attention. As a result it has been found that penetration of the agglomerated toner between the toner carrier and a sealant is suppressed, wear of the toner carrier and the accompanying toner leakage is prevented and at the same time, steadily favorable image is obtainable even in a working environment more prone to cause defective image including long-term preservation and long-term service by regulating the physical properties of the surface of the toner carrier so that the xe2x80x9cspecific creep-valuexe2x80x9d is made to be in the under-mentioned range, said value being obtained from the measurement of deformation restoration behavior of the surface of the toner carrier at the time of measuring the universal hardness under a measuring condition at a definite load with respect to the toner carrier having an elastic layer and a coating layer composed of single layer or a plurality of layers, said layer/s being formed outside the above-mentioned elastic layer directly or through another layer.
In the case of obtaining the universal hardness in the same manner as the foregoing, by pushing a penetrator in the object to be measured under a measuring condition at a definite load, then preserving the definite load environment, and thereafter gradually decreasing the test load applied by the penetrator, it is made possible to obtain the difference in the position of the penetrator which difference is caused by the plastic deformation of the object to be measured between the initial measurement stage and the time of ending the measurement. The difference therebetween is referred to as for instance, xe2x80x9c60 sec. creep value under measuring condition at a definite load of 100 mN/mm2xe2x80x9d in the case of the definite load being 100 mN/mm2 and the preservation time at a definite load (creep time) being 60 sec. It has been found that the creep value is caused by the plastic deformation of the toner carrier due to the above-mentioned measurement of deformation restoration behavior, and that the degree of penetration of the agglomerated toner between the toner carrier and a sealant and the degree of accompanying wear of the toner carrier can be standardized, for instance, by the equivalent value obtained by measuring universal hardness by the use of, for instance, a hardness measuring instrument available on the market such as a ultracompact hardness tester ( manufactured by Fischer Corporation under the trade name H-100V). The present invention has been accomplished by the above mentioned findings and information.
In addition, intensive research and investigation were set forward by the present inventors on the problem that in the case where a toner carrier is incorporated in an image formation apparatus and is used for a long period of time, while being accompanied by an increase in the number of printed sheets, there are caused fogging of white image, roughness in half tone image or unevenness in density of black image. As the results, the following three items have been confirmed.
(1) In order to obtain steadily high quality images for a long period of time, it is indispensable that toner properties remain unchanged even under the condition of long-term running.
(2) A toner undergoes stress due to agitation at all times in a developer tank, in particular undergoes maximum stress at portions between the toner carrier and a layer regulating blade and between the toner carrier and a toner supply member, and in the case of long-term running, deterioration of the toner is promoted at the portions mentioned above.
(3) Strong stress, when imposed on a toner, causes deformation and cracking of toner particles, peeling of an external additive and the like, whereby prescribed charge quantity is no longer assured. Consequently overall charge distribution becomes non-uniform, thus bringing about such defective image as fogging of white image, roughness of half tone image and unevenness in density of black image.
In particular, it has been elucidated during the course of the research by the present inventors that the deterioration of the toner is markedly promoted when the toner carrier has a high hardness in close vicinity to the surface thereof.
In the meanwhile, the hardness of a toner carrier has heretofore been usually evaluated by the extent of deformation when a relatively large definite load of approximately one kg is applied thereto as typified by Asker C and JIS A.
According to the research by the present inventors, however it has been elucidated that a toner moving on a toner carrier causes only slight deformation, and the strength of the stress imposed on the toner is not due to a conventional hardness such as Asker C hardness, but is greatly influenced by the hardness upon slight deformation on the surface of the toner carrier or in close vicinity to the surface thereof. Moreover, universal hardness is suitable as an index which denotes the hardness in close vicinity to the surface of the toner carrier, and it is made possible to effectively prevent the deterioration of the toner by limiting the value of the universal hardness within a definite range. As a result, such limitation led to success in assuring steadily high quality image for a long period of time. Thus the present invention has been accomplished through the circumstances as described hereinbefore.
That is to say, the present invention provides:
A toner carrier (I) which supports a toner on its surface to form thin films thereof and in this state, supplies the toner to the surface of an image formation body in contact with or in close vicinity to said image formation body so as to form visible image thereon, said toner carrier having at least 0.70 of Z value, which is represented by the formula (1) obtained from deformation restoration behavior of the surface of said toner carrier at the time of measuring the universal hardness of the surface thereof:
xe2x80x83Z=We/(We+Wr)xe2x80x83xe2x80x83(1)
wherein We is elastic energy from among the energies in relation to the deformation of the surface thereof, said elastic energy being obtained from deformation restoration behavior of the surface of said toner carrier at the time of measuring the universal hardness of the surface thereof; and Wr is plastic energy therefrom;
An image formation apparatus comprising, as a minimum requirement, a toner carrier and an image formation body on the surface of which is formed a visible image by means of a toner supplied from the toner carrier and which is in contact with or in close vicinity to the toner carrier forming a toner thin film on the surface thereof, said image formation apparatus being equipped with said toner carrier (I);
A toner carrier (II) which supports a toner on its surface to form thin films thereof and in this state, supplies the toner to the surface of an image formation body in contact with or in close vicinity to the image formation body so as to form visible image thereon, said toner carrier having at most 10.0 xcexcm of 60 sec. creep value obtained from deformation restoration behavior of the surface of said toner carrier under measuring condition at a definite load of 100 mN/mm2 at the time of measuring the universal hardness of the surface thereof;
An image formation apparatus comprising, as a minimum requirement, a toner carrier and an image formation body on the surface of which is formed a visible image by means of a toner supplied from the toner carrier and which is in contact with or in close vicinity to the toner carrier forming a toner thin film on the surface thereof, said image formation apparatus being equipped with said toner carrier (II);
A toner carrier (III) which supports a toner on its surface to form thin films thereof and in this state, supplies the toner to the surface of an image formation body in contact with or in close vicinity to the image formation body so as to form visible image thereon, said toner carrier having at most 3 N /mm2 of universal hardness at a depth of at most 5 xcexcm from the surface of said toner carrier under measuring condition at a definite load applying rate of 100/60 (mN/mm2/sec.) at the time of measuring the universal hardness of the surface thereof; and
An image formation apparatus comprising, as a minimum requirement, a toner carrier and an image formation body on the surface of which is formed a visible image by means of a toner supplied from the toner carrier and which is in contact with or in close vicinity to the toner carrier forming a toner thin film on the surface thereof, said image formation apparatus being equipped with the toner carrier (III).